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Thread: How to make framebuffer look like a real monitor?

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  1. #1
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    Default How to make framebuffer look like a real monitor?

    Is there a way to make X treat Linux framebuffer device (e.g. /dev/fb0 backed by virtual framebuffer) as a real display? Ideally it should appear in system display settings as a configurable monitor. Does it require writing some kernel code or it's possible to somehow get away with for example editing X config files or using xrandr? If yes, is there a way to do this after boot (hotplug)?
    Thank you for any advice and related information.

  2. #2
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    If that framebuffer is created using kernel modesetting, then you can use it with xf86-video-modesetting as xrandr 1.4 output slave.

    Else you can use xf86-video-fbdev, but that will only work with xinerama and you will lose all acceleration.

  3. #3
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    Quote Originally Posted by chithanh View Post
    If that framebuffer is created using kernel modesetting, then you can use it with xf86-video-modesetting as xrandr 1.4 output slave.

    Else you can use xf86-video-fbdev, but that will only work with xinerama and you will lose all acceleration.
    Well, there's no framebuffer yet, I need to write one.. More precisely, the following is needed: virtual graphics adapter, that looks like real one to the system (so that it's possible to drag windows onto it, it appears in system display settings, etc) but that does not do any real rendering and only has framebuffer in RAM.

    As I understand, there are following options:

    1) Write DRM driver with modesetting support. Most proper way, but rather complex for someone unfamiliar with graphics stack. May be I could use SimpleDRM as a starting point here?
    2) Use old virtual framebuffer module (vfb.c) together with fbdev X.org driver. Hotplug won't probably work, also it will probably require manual editing of xorg.conf which sort of makes it usable only for home use.
    3) May be writing X.org driver only could be enough?

    Sorry for newbie questions, I spent few days googling and reading about Linux graphics stack but it still looks mysterious

  4. #4
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    Quote Originally Posted by ivand View Post
    Well, there's no framebuffer yet, I need to write one.. More precisely, the following is needed: virtual graphics adapter, that looks like real one to the system (so that it's possible to drag windows onto it, it appears in system display settings, etc) but that does not do any real rendering and only has framebuffer in RAM.

    3) May be writing X.org driver only could be enough?
    Xorg already has a xf86-video-dummy driver that does most of this - you might want to add the missing bits you need to it rather than start from scratch.

  5. #5
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    Quote Originally Posted by chithanh View Post
    If that framebuffer is created using kernel modesetting, then you can use it with xf86-video-modesetting as xrandr 1.4 output slave.

    Else you can use xf86-video-fbdev, but that will only work with xinerama and you will lose all acceleration.
    Well, there's no framebuffer yet, I need to write one.. More precisely, the following is needed: virtual graphics adapter that looks like a real one to the system (it's possible to drag windows onto it, it appears in system display settings, etc). However instead of actual rendering it only fills framebuffer in memory. Hotplug and multiple adapters are desirable.
    As I understand, there are following options:

    1) DRM driver with modesetting support. Most proper way, might be somewhat complex someone unfamiliar with kernel graphics stack though. Could I use SimpleDRM here as a starting point?
    2) Old virtual framebuffer driver (vfb.c) combined with X.org fbdev driver. This works in theory, however looks like there's no hotplug and editing xorg.conf might be the only option, which greatly limits applicatbility.
    3) May be writing X.org driver only could do the job, w/o writing any kernel code?

    Thank you and sorry for newbie questions here, I spent days reading about Linux graphics stack but it still looks unclear.

  6. #6
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    Sorry for duplicate post, I thought it got lost due to some glitch. Please delete this one and one of the two above if possible. Thanks.

  7. #7
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    There's virtually no moderation on phoronix forums

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